Hello, I have a case which I need to retrieve data from local first then show it, after that retrieve data from API, then override local data, then show the updated version. I started with concat operator and it doesn't work I think because first time there is no local data to get

concat will trigger the second stream only if the first completed

Yes I figured that out

try this:

database.publish{
  Observable.concat(it.take(1), Network, it.skip(1))
}

Is there any other operator that skip the first stream if it doesn't emit any data

why?

This honestly is wrong, you should always expose only local data as observable, and then have the api request only write to local -> triggering emit of the local data observable; no need to concat etc

yeah that is the next level, when you just observe the database changes and also trigger an event to request network which updates the database

I did it with publish and merge and take until, following Kushak example in his Rxjava be examples repo